The present invention relates to a confocal scanning endoscope system having a confocal observation function.
Confocal scanning microscope systems capable of providing highly magnified high resolution images have been used. The confocal scanning microscope system is configured to emit a laser beam scanning on a sample in two dimensions. An operator of the confocal scanning microscope system observes the sample through a highly magnified high resolution observation image formed by the confocal scanning microscope system by illuminating the sample with the laser beam and receiving the laser beam from the sample through a pinhole positioned at a point conjugate with the sample. Examples of such a confocal scanning microscope system are disclosed in Japanese Patent Provisional Publications Nos. 2000-275528A and 2004-138947A.
The above mentioned confocal microscope system requires an operator to remove part of tissue in a body cavity of a subject using an endoscope so that the removed part of the tissue can be observed using the confocal scanning microscope system. That is, the confocal observation requires the operator to conduct troublesome work in which removal of tissue and the observation of the tissue have to be conducted using separate apparatuses.
For this reason, an endoscope system having the above mentioned function of the confocal scanning microscope system is desired. Such an endoscope system (hereafter, referred to as a confocal scanning endoscope system) is able to reduce a load on the operator during observations. Because the confocal scanning endoscope system is configured to move light in two dimensions on tissue, there is a case where the light passes through a peripheral region of a confocal optical system provided in the confocal scanning endoscope system. Because the peripheral region of the confocal optical system causes aberrations in a larger amount than a central region of the confocal optical system, light-gathering power of the confocal optical system decreases in the peripheral region. Therefore, resolution and brightness of a part of an image formed in the confocal scanning endoscope optical system by the light passing through the peripheral region of the confocal optical system decrease, and thereby a peripheral part of an observation image may become blurred.
Using the confocal scanning endoscope system, the operator attempts to find abnormality of tissue, for example, based on change of a shape of a cell while observing the observation image displayed on a monitor of the confocal scanning endoscope system. If a blurred part appears on the observation image due to the above mentioned factors specific to the confocal scanning endoscope system, the diagnosis by the operator may be adversely affected.
As in the case of a normal endoscope system, the confocal scanning endoscope system is required to reduce the diameter of an insertion tube which is inserted into a body cavity of a subject by downsizing the confocal optical system so that a load on the subject during the diagnosis can be reduced.
However, downsizing an optical system leads to increasing the amount of off-axial aberration. In other words, downsizing the confocal optical system for decreasing the diameter of the insertion tube, the blurred part in the observation image may become larger. Further, if the confocal optical system has positional errors, such as decentering, the blurred part appears on the observation image in a shape asymmetric about an optical axis of the confocal optical system. Such deterioration of the observation image may also adversely affect the diagnosis by the operator.